Response of the bark beetle, Hylesinus pruinosus, to the male-produced pheromone, endo-brevicomin

Hylesinus pruinosus Eichhoff (Coleoptera: Curculionidae) females solitarily attacking pieces of green ash produced exo-brevicomin, while males paired with them produced endo-brevicomin. These pheromones were also produced following the application of juvenile hormone III. This ash bark beetle was strongly attracted to traps baited with endo-brevicomin (either the pure (+)-enantiomer or racemate) in the absence of other semiochemicals, but was attracted only weakly (if at all) to exo-brevicomin. The sex ratio in response to endo-brevicomin was approximately 50:50. Large antennal responses to both endo- and exo-brevicomin were recorded for male and female H. pruinosus. As the genus Hylesinus is reported to be bigynous with females acting as the pioneer sex, our data may illustrate an instance in which the secondarily-arriving sex of a bark beetle produces the more potent aggregation pheromone.